The present disclosure relates to an inspection technique for sheet detection devices including reflective optical sensors for detecting sheets such as documents and print sheets that are conveyed or placed in image processing apparatuses such as image forming apparatuses and image reading apparatuses.
For image processing apparatuses such as multifunction peripherals and copying machines, a reflective optical sensor is used for detecting a size of a document to be read or determining whether or not a document is in a predetermined detection area. The reflective optical sensor applies light to a document to be detected, and receives light reflected by the document. The received-light signal is outputted as an output signal from the reflective optical sensor, and is used for detecting the size of the document or determining whether or not the document is in the predetermined detection area.
The output signal from the reflective optical sensor varies according to an image density in a document to be detected, and a distance to the document. That is, the brighter the image in the document to be detected is, the greater a value of the output signal from the reflective optical sensor is. Further, the less a distance between the reflective optical sensor and the document to be detected is, the greater the value of the output signal therefrom is.